The bedrock in the Kvarken region is ancient. It formed during the Proterozoic era about 2 to 1.3 billion years ago. Since then, the bedrock has been worn by erosion, then covered by sediment and eroded once again. The past two million years, the Quaternary period, are characterised by repeated ice ages alternating with warmer periods.
Most of the layers of loose soil in Sweden and Finland arose during and after the last ice age, which ended about 10,000 years ago. The inland ice scraped away and dragged with it vast amounts of loose material, clay, sand, gravel, rocks and boulders. When the ice melted this material was sorted and deposited in various ways. This mixture of soil, known as moraine, usually covers the bedrock first and its topography typically follows the bedrock's contours. The moraine has also been deposited in various formations, giving the visible landscape in Kvarken its unique appearance. The most important of these moraine formations are shown below:
Drumlins are oval, elongated moraine ridges that formed under the ice. They run parallel to the direction of the moving ice. Individual drumlins are usually 2 to 4 metres high, about a hundred or so metres wide and sometimes several kilometres long. They are often found in fields or groups called swarms. Drumlins are especially well developed on the western side of Kvarken, including in the Skeppsvik archipelago.
End moraines have formed along the margin of the inland ice. End moraines can be large or small, long or short. They are often asymmetrical, with a gentle slope on the stoss (proximal) side and a steeper slope on the lee (distal) side.
De Geer moraines are closely related to end moraines. According to the most recent theory, they formed in crevasses running parallel to the ice margin in sub-aquatic conditions. De Geer moraines are often found in clusters in level areas. The ridges are a few hundred metres long and about 5 metres high. Especially well-developed De Geer moraines can be found in the Replot and Björkö areas on the eastern side of Kvarken.
Hummocky moraines occur in lowland areas. They are 5 to 20 metres high and do not run in any particular direction. They form a mosaic landscape where the individual hummocks are surrounded by bogs and marshlands. Hummocky moraines in Kvarken formed beneath the melting glacier. A Rogen moraine is a type of hummocky moraine that mainly runs perpendicular to the direction in which the ice moved.
The thick ice sheet, which was three kilometres at its thickest, pressed the earth's crust 800 to 1,000 metres downward. When the ice began to melt the crust began to lift to reach its previous position. The land uplift rate in Kvarken is currently 8 to 8.5 mm per year. At this rate, the flat coastal and archipelago landscape noticeably changes during a single generation. Bridges and boathouses wind up on dry land, waterways become shallow, inlets are cut off from the sea and new underwater banks emerge. Scientists expect the land to rise another 100 to 125 metres. In about 2,500 years this will result in a land bridge across the Kvarken strait. The development will be quite different if the greenhouse effect becomes reality, with the level of the sea rising as the polar ice cap begins to melt due to global warming. This scenario would counter the effects of the land uplift.
Terranova - Kvarken Nature Centre